Tris(isocyanatotolyl) isocyanurate-tolylene diisocyanate complexes

ABSTRACT

An aromatic polyisocyanate which is a molecular complex consisting of one molecule of tris(isocyanatotolyl) isocyanurate associated with two molecules of tolylene diisocyanate. The complex, which is a free-flowing crystalline powder low in toxicity, reacts with active-hydrogen containing compounds to form polyurethane coatings, foams, elastomers, etc. Such polyurethane coatings have particularly outstanding resistance to weather exposure and solvent attack.

United States Patent Irwin [54] TRISGSOCYANATOTOLYL) ISOCYANURATE-TOLYLENE DIISOCYANATE COMPLEXES [72] Inventor: Carl Francis Irwin, New Castle, Del.

[73] Assignee: E. I. du Pont de Nemours and Company,

Wilmington, Del.

[22] Filed: Oct. 26, 1970 [21] Appl.No.: 84,150

[52] U.S. Cl ..260/7S NT, 260/2.5 AW, 260/77.5 NC,

260/858 [51] Int. Cl. ..C08g 22/18, C088 22/28 [58] Field of Search ..260/77.5 NC, 248 NS, 858, 75 NT [56] References Cited UNITED STATES PATENTS 3,; 17,002

[151 3,666,725 [4 1 May 30, 1972 2,978,449 4/1961 France et al. .....260/248 3,252,942 5/1966 France et al. ....260/77.5 3,487,080 12/ i969 Matsui et al. ..260/248 3,573,259 3/1971 Argabright et al ..260/77.5

Primary Examiner-Donald E. Czaja Assistant Examiner-H. S. Cockeram Attorney-Vemon R. Rice [57] ABSTRACT 10 Claims, No Drawings TRISGSOCYANATOTOLYL) ISOCYANURATE- TOLYLENE DIISOCYANATE COMPLEXES BACKGROUND OF THE INVENTION Polyisocyanates are highly useful compounds which have gained wide acceptance as starting materials in the manufacture of useful products such as foams and coating materials. The isocyanates most extensively used are aromatic diisocyanates such as 2,4-tolylene diisocyanate (or a mixture thereof with 2,6-tolylene diisocyanate) and 4,4- methylenebis(phenyl isocyanate), or crude mixtures containing the above isocyanates and various by-products produced during the manufacture of the isocyanates.

Although many of the known aromatic isocyanates are more or less suitable for use in preparing products such as polyurethane coatings and foams, there is a need for a polyisocyanate which has a functionality (isocyanato groups per molecule) greater than two. Isocyanates having higher functionalities generally yield faster curing coatings which are tougher and more stable against outdoor exposure and certain solvents than coatings prepared from lower-functional isocyanates. Foams prepared from higher functional isocyanates generally develop gel strength more rapidly and manifest improved compression set. Another highly desirable attribute of any isocyanate is low volatility (and thus low toxicity) at normal operating temperatures. Few, if any, of the known aromatic polyisocyanates combine all these attributes.

SUMMARY OF THE INVENTION This invention provides an aromatic polyisocyanate which is a molecular complex represented by the formula wherein X,, X, and X, are independently a 3-isocyanato-4- methylphenyl radical, a 3isocyanato-Z-methylphenyl radical or a 5isocyanato-2-methylphenyl radical and Y is 2,4-tolylene diisocyanate or 2,6-tolylene diisocyanate.

DETAILED DESCRIPTION The molecular complex of this invention (hereinafter called complex" consists of a tris(isocyanatotolyl) isocyanurate molecule (tolylene diisocyanate trimer) in association with two molecules of tolylene diisocyanate (TDI). The complex thus contains seven free isocyanato groups. Either of the tolylene diisocyanate isomers, 2,4- or 2,6-, can be included either in the TDl trimer or as the TD] molecules associated with the trimer. The preferred complexes are formed from mixtures of 2,4- and 2,6-TDI, usually in about an 80:20 ratio.

The complexes can be prepared by adding to tolylene diisocyanate a trimerization catalyst, e.g., tetramethylguanidine or tertiary amines such as triethyl amine or 2,4,6-

tri(dimethylaminomethyl) phenol and heating the mixture to about 50-70 C. to form TDI trimer. After the mixture contains about percent by weight or more TDl trimer, the catalyst is rendered inactive by adding acids such as hydrogen chloride and phosphoric acid or acid halides such as phosgene, benzoyl chloride or acetyl chloride. The reaction mass is allowed to cool to room temperature and kept at room temperature for 24-48 hours during which the complex crystallizes. The complex is then filtered, washed and dried. In preparing the complex, the temperature of the trimer-TDI mixture in which the complex forms should be below the melting point of the complex since melting causes the complex to at least partially dissociate. In order to isolate the complex from a trimer-TDI mixture, the concentration of TDI and trimer in that mixture must be such that the complex is to some extent insoluble in the mixture and thus precipitates out. In general, the complex will precipitate from any trimer-TDI mixture containing about 20 percent by weight or more trimer. The complex can be formed in the presence or absence of a solvent. If a solvent is used, however, it must be a substance in which the complex does not appreciably dissociate, such as toluene or hexane.

The complexes are free flowing crystalline powders which melt over a narrow temperature range, the exact melting point depending on the TDl molecules which form the complex. Complexes formed entirely from 2,4-TDI molecules melt at about 7275 C. and complexes formed entirely from 2,6-TDI molecules melt at about l25l32 C. Complexes made from mixtures of 2,4- and 2,6-TDl melt at temperatures intermediate the 2,4 and 2,6-TDl complexes. The complexes are soluble in esters such as ethyl acetate, ketones such as acetone, and aromatic hydrocarbons such as benzene and toluene, but are relatively insoluble in aliphatic hydrocarbons such as n-hexane in which the complexes form a slurry. The complexes tend to dissociate to a considerable extent in esters and ketones but substantially maintain their integrity in aromatic and aliphatic hydrocarbons and halogenated hydrocarbons.

The complex can be destroyed by heating to a temperature sufiiciently high to distill the TDl, leaving the TD! trimer. The TDl distillate recovered from this heating process is the quantity needed to complex with the trimer in the amount of two molecules of TDI per molecule of trimer. The infrared spectrum of the complex in chloroform matches the spectrum of a chloroform solution of 1 mole of TDI trimer and 2 moles of TDI at equal solute concentrations.

The complexes of this invention provide a polyisocyanate of high functionality in a conveniently-handleable physical form. Because the vapor pressure of the solid complex or certain solutions of the complex is almost nil, the complex has very low toxicity in comparison with other polyisocyanates such as TDl.

The complex can be used to prepare polyurethane products such as coatings and foams by reacting the complex with active-hydrogen containing compounds such as polyols, polyamines and water by techniques well known in the art.

The usual polyether and polyester polyols can be employed in preparing polyurethanes based on the trimer-complexes. Representative polyols are polyalkyleneether glycols such as polyethyleneether glycol, polypropyleneether glycol and polytetramethyleneether glycol and the polyethers prepared by the copolymerization of cyclic ethers such as ethylene oxide, propylene oxide, trimethylene oxide and tetrahydrofuran with aliphatic polyols such as ethylene glycol, 1,3-butanediol, glycerol and 'sorbitol; polyester glycols prepared by the polymerization of cyclic lactones such as e-caprolactone or by the condensation polymerization of a dicarboxylic acid and a molar excess of an organic polyol, representative diacids being succinic, glutaric and adipic acids and representative organic polyols being ethylene glycol, propylene glycol, 1,3-butanediol and 1,4-butanediol.

lt is also possible to employ as at least part of the polyol component, an aliphatic polyol having a low molecular weight such as ethylene glycol, 1,4-butanediol, trimethylol propane and glycerol. Polyamines such as methylenedianiline, mtolylene diamine, 4,4'-methylene-bis(o-chloroaniline), hexamethylenediamine and the crude methylenebridged polyarylene polyamines prepared by condensing aromatic diamines and formaldehyde can also be used as part of the active hydrogen containing compounds. Other representative polyols are given in U.S. Pat. No. 3,248,373 to Barringer. Detailed information on formulations and procedures for preparing representative urethane coatings, elastomers, adhesives and flexible foams can be found in Chapters VII, IX, X and XI of Polyurethanes: Chemistry and Technology, Part II," Saunders and Frisch, lnterscience Publishers (1964).

Typical of the coatings that can be prepared by the complexes of this invention are the moisture-cure coatings prepared by reacting about 1.6-2.0 equivalents of the complex with one equivalent of a polyether or polyester glycol having a molecular weight of about 200-1000. Alternatively, mixtures of polyether or polyester glycols with low molecular weight diols, said mixtures having average molecular weights of 200-1,000, can be used. The resulting reaction product when mixed with conventional coating solvents and curing catalysts can be applied by spraying, brushing or dipping and will cure in air. Two part coatings can be made in similar fashion, but cure is usually effected by adding about an equivalent amount of a low molecular weight diol to the solvent solution of the reaction product of polyisocyanate and glycol.

Flexible foams are preferably prepared by a quasi-or fullprepolymer procedure in which an excess of trimer complex is first reacted with a polyether or polyester diol and/or triol having an equivalent weight of about 500-1 ,500 to prepare an isocyanato-terminated prepolymer. By adding water (or in the case of quasi-prepolymer systems, water plus polyol) in amounts up to about equivalent to the available NCO in the prepolyrner, the foam is formed. Rigid and semi-rigid foams can be similarly prepared by using polyols having lower equivalent weights and functionalities of at least about 3.

The trimer-complexes of this invention yield polyurethane coatings which are tougher and more stable against outdoor exposure and certain solvents than are coatings prepared from other aromatic diisocyanates such as TDl.

The invention is further illustrated by the following examples wherein parts and percentages are by weight unless otherwise indicated.

EXAMPLE 1 The following procedure is used to prepare complexes of tolylene diisocyanate (TDl) trimer and TDI from the TD! compositions listed below:

A. 2,4-TD1 B. 80 percent 2,4-TDI; 20 percent 2,6-TDl C. 60 percent 2,4-TD1; 40 percent 2,6-TDI D. 2,6-TDl A mixture of 620 g. of TD] and 0.175 g. of 2,4,6- tris(dimethylaminomethyl) phenol was heated to 70 C. and agitated at 70 C. until the --NCO content of the reaction mass dropped to 35-36 percent. This decrease in -NCO content corresponds to the formation of about 50-55 percent by weight of TDI trimer. The reaction is stopped by the addition of 0.2 g. of benzoyl chloride. The reaction mass is allowed to cool to room temperature and kept at room temperature for 24-48 hours to permit the complex to crystallize. The thick mass is then agitated vigorously with 620 g. of a 1:] solution by volume of n-hexane and the same TDl used in the trimerization. The resulting slurry is filtered and the solids are washed with about 200 g. of the 1:1 hexane-TDl solution and then with about 1,200 g. of n-hexane. The solid complex is air dried.

The following complexes are prepared by the above general procedure.

Initial 'IDI composition A B B C D Isolated yield of complex,

percent 47.5 30 B 32 33 -NCO in complex, percent (cele, 33.8%) 33. 4 33. 5 33, 2 32. 4 32. 2 Mel ing range, C. 72-75 86-89 102-104 97-107 125-132 Isorner ratio of TDI distilled from complex, percent 2,4-

TDI 100 90 86 86.6 0

I Yield reduced by washing with more solvent than used in general procedure.

b Used 1.225 g. of 2,4,6-tris(dimethylaminomethyl)-phenol and 1.5 g. of benzo l chloride.

" A; determined by amine equivalent, ASTM-D1638-6OT.

The complexes have no odor of TDI.

Solvent They are further characterized by the following procedures and tests:

1. Quantitative determination of TD] in complex About 1.5 g. of complex B is weighed accurately into a distillation flask and 150 cc. of dimethyl phthalate is added. About 75 cc. of material is distilled from the flask at from 20 mm Hg pressure during which distillation the temperature ranges from 150 C. up to 166 C. The -NCO content of the distillate corresponds to a recovery of TD! equivalent to 100.4 percent of the TDl which would be contained in a complex of 1 mole of TD] trimer and 2 moles of TDI. When this procedure is repeated, the recovery of TD! is 99.8 percent of the calculated amount.

2. Infrared spectrum The infrared spectrum of the complex in chloroform matches the spectrum of a chloroform solution of 1 mole of TD] trimer and 2 moles of TDI at equal solute concentrations.

3. Vapor pressure measurements Using a Uni-jet TDl vapor detector, sold by Union Industrial Equipment Corporation, Fall River, Mass, the concentration of TD] vapors was determined in the gas phase over a series of solutions of the complex in different solvents. For comparison, similar measurements were made using TDl as the solute.

Concentration TDI in vapor,

Solute p.p.m.

Ethyl acetate, 25 ml TDl, 1.2 gl

D Complex B, 3 g

Complex B, 6 g.

1 Equivalent to quantity of TDl contained in 3 g. of complex. 2 Complex is relatively insoluble in n-hexane and sample is a slurry.

The results indicate that the complex partially dissociates when it is dissolved in a solvent. The results further indicate that TD] and TD! trimer do not form a complex immediately when dissolved in a solvent. The absence of any dissociation in hexane indicates that the solid complex is quite stable at room temperature as further shown by the fact that the Uni-jet TDl detector gives a zero reading for the vapor above the complex in a closed container.

EXAMPLE 2 The following ingredients are added to an agitated reaction vessel to prepare a one-part moisture-curing urethane coating.

Polypropylene ether glycol 100.0 parts Butanediol l,3 9.0 parts 2-Ethoxyethyl acetate 51.5 parts Xylene 51.5 parts Benzene 10.0 parts Benzene and traces of water contained in the formulation are removed by distillation. The distillation is stopped after 10 pans of distillate has been collected. The temperature of the reactor contents is lowered to 30 C. and 46.0 parts of TD!- TDl trimer complex B of Example 1 is added to the formulation. The temperature of the reaction mass is raised to -95 C. over a period of 30 minutes and maintained at 90-95 C. for about 3 hours. The reaction mass is then cooled to about 25 C. and about parts of additional xylene is added to reduce the solids or non-volatile content of the coating composition to 40 percent by weight. 1n addition, 1.5 parts of an ultraviolet light absorber, 2,2'-dihydroxy-4,4-dimethoxybenzophenone, is added and mixed into the coating composition.

Three coats of the composition are applied by brush to 6 X 12 inch unprimed maple panels allowing 24 hours between coats. For comparison, three coats of commercial tung phenolic spar varnish are applied to unprimed maple panels. The test panels are exposed for 6 months at Hialeah, Florida at an angle of 45 facing south. At the end of the exposure, the panels coated with the urethane coating of this example have retained considerable gloss and the coating is intact. in contrast, the control spar varnish coated panels have lost their gloss and the coating is beginning to fail at the edges of the panel as evidenced by cracking.

What is claimed is:

1. An aromatic polyisocyanate composition consisting essentially of at least one tris-(isocyanatotolyl) isocyanuratetolylene diisocyanate complex of the formula derived from 2,6-tolylene diisocyanate.

4. A composition of claim 1 wherein the complex is formed from a mixture of 2,4- and 2,6-tolylene diisocyanates.

5. A polyurethane prepared by reacting the composition of claim 1 with at least one compound containing at least two Zerewitinoff hydrogens.

6. A polyurethane prepared by reacting the composition of claim 2 with at least one compound containing at least two Zerewitinoff hydrogens.

7. A polyurethane prepared by reacting the composition of claim 3 with at least one compound containing at least two Zerewitinoff hydrogens.

8. A polyurethane prepared by reacting the composition of claim 4 with at least one compound containing at least two Zerewitinofi" hydrogens.

9. A coating composition according to claim 5 wherein the polyurethane is prepared by mixing about 1.6-2.0 equivalents of the polyisocyanate complex with about 1 equivalent of a polyether or polyester glycol having a molecular weight of about 200-1000 or with about 1 equivalent of a polyether or polyester glycol in admixture with a low molecular weight diol, said mixture having an average molecular weight of about 200-1000.

10. A coating composition according to claim 8 wherein the polyurethane is prepared by mixing about l.62.0 equivalents of the polyisocyanate complex with about 1 equivalent of a polyether or polyester glycol having an average molecular weight of about ZOO-1,000 or with about 1 equivalent of a polyether or polyester glycol in admixture with a low molecular weight diol, said mixture having an average molecular weight of about ZOO-1,000. 

2. A composition of claim 1 wherein the Y molecules are 2,4-tolylene diisocyanate and the X1, X2 and X3 radicals are derived from 2,4-tolylene diisocyanate.
 3. A composition of claim 1 wherein the Y molecules are 2,6-tolylene diisocyanate and the X1, X2 and X3 radicals are derived from 2,6-tolylene diisocyanate.
 4. A composition of claim 1 wherein the complex is formed from a mixture of 2,4- and 2,6-tolylene diisocyanates.
 5. A polyurethane prepared by reacting the composition of claim 1 with at least one compound containing at least two Zerewitinoff hydrogens.
 6. A polyurethane prepared by reacting the composition of claim 2 with at least one compound containing at least two Zerewitinoff hydrogens.
 7. A polyurethane prepared by reacting the composition of claim 3 with at least one compound containing at least two Zerewitinoff hydrogens.
 8. A polyurethane prepared by reacting the composition of claim 4 with at least one compound containing at least two Zerewitinoff hydrogens.
 9. A coating composition according to claim 5 wherein the polyurethane is prepared by mixing about 1.6-2.0 equivalents of the polyisocyanate complex with about 1 equivalent of a polyether or polyester glycol having a molecular weight of about 200-1000 or with about 1 equivalent of a polyether or polyester glycol in admixture with a low molecular weight diol, said mixture having an average molecular weight of about 200-1000.
 10. A coating composition according to claim 8 wherein the polyurethane is prepared by mixing about 1.6-2.0 equivalents of the polyisocyanate complex with about 1 equivalent of a polyether or polyester glycol having an average molecular weight of about 200-1,000 or with about 1 equivalent of a polyether or polyester glycol in admixture with a low molecular weight diol, said mixture having an average molecular weight of about 200-1,000. 